EFFECT OF FRICTION AND LUBRICATION IN DEEP DRAWING

Abstract

Forming process is a very economical process as the desired shape, size and finish can be obtained without any significant loss of material. So the wastage of material in metal working processes is either negligible or very small, and the production is in general is very high. These two factors give rise to the economy in production. Moreover, a part of input energy is utilized in improving the strength of the product. Deep drawing is a simple non-steady state sheet metal forming process for making seamless shells, cups and boxes of various shapes. Though the process is simple it has several parameters determining the outcome and the analysis of the process can be complex. The parameters include the draw ratio, die and punch radii, blank holder force, blank holder and die friction and lubrication, material properties, such as the stress–strain curve, anisotropy, grain size, etc. To produce cups of satisfactory quality the right combination of the parameters must prevail in the drawing process. The maximum draw ratio possible is governed by the material properties, the stress needed to radially draw the metal into the die cavity, frictional resistances at the flange of the cup being drawn and at the die radius and the bending and unbending at the die radius. The drawing force and the energy needed are provided by the punch. Variations to the simple or conventional deep drawing processes make use of flexible tool materials such as urethane, hydraulic pressure or other aids. In deep drawing process, the various defects are occurred in the forming of cups such as
wrinkling in flange, wrinkling in wall, tearing, earing, localized necking and fracture. The blank is drawn radially inwards the flange undergoes radial tension and circumferential compression. The latter may cause wrinkling of the flange if the draw ratio is large, or if the cup diameter-to-thickness ratio is high. A blank-holder usually applies sufficient pressure on the blank to prevent wrinkling. Radial tensile stress on the flange being drawn is produced by the tension on the cup wall induced by the punch force. Hence, when drawing cups at larger draw ratios, larger radial tension are created on the flange and higher tensile stress is needed on the cup wall. Bending and unbending over the die radius is also provided by this tensile stress on the cup wall. In addition, the tension on the cup wall has
to help to overcome frictional resistance, at the flange and at the die radius. As the tensile stress that the wall of the cup can withstand is limited to the ultimate tensile strength of the material. In this paper presents the parametric study on deep drawing with presentations with influence of friction and lubrication to be studied.